8101 Datasheet, PDF (46/172 Pages) LSI Computer Systems – Gigabit Ethernet Controller

2.11.2 8B10B Decoder
The 8B10B decoder performs the reverse process of the 8B10B encoder.
The 8B10B decoder converts each 10-bit word back into an 8-bit byte
using the code conversion tables defined in IEEE 802.3z and shown in
Table 2.7 (in abbreviated form) and Table 2.8. The 8B10B decoder also
checks the running disparity of the incoming 10B word to insure that it is
correct.
A PCS codeword error results if the 8B10B decoder detects any of the
following:
• A 10B word that is not valid (does not appear in Table 2.7)
• An ordered set that is not valid (does not appear in Table 2.8)
• An error in the running disparity
Packets with PCS codeword errors are normally discarded. Refer to
Section 2.13, “Packet Discard” for more details on discards. Clearing the
DIS_CWRD bit in “Register 8–Configuration 2‚" Section 4.3.9, programs
the controller to not discard a packet with PCS codeword errors.
Table 2.8 10B Defined Ordered Sets
10B Code
Symbol
/C1/
/C2/
/C/
/I1/
/I2/
/I/
Description
Link
Configuration 1
Link
Configuration 2
Link
Configuration
Idle 1
Idle 2
Idle
10B Codes
/K28.5/¹
/D21.5/
config_word1
config_word2
/K28.5/¹
/D2.2/
config_word1
config_word2
Alternating
/C1/ & /C2/
/K28.5/
/D5.6/
/K28.5/
/D16.2/
/I1/ or /I2/
Begin
End
RD
RD
+ or -
flip²
+ or −
same²
–
–
+
–
–
–
–
–
2-28
Functional Description
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